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Nerves & Neurons

Nerves & Neurons

Author: Rebecca Newburn

Learn about the nervous system and tissues that make it up.

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Before You Start

How does your brain get and share information?

What are the structures and functions of nerves?

The Nervous System

A small child darts in front of your bike as you race down the street. You see the child and immediately react. You put on the brakes, steer away from the child, and yell out a warning, all in just a split second. How do you respond so quickly? Such rapid responses are controlled by your nervous system. 

The nervous system is a complex network of nervous tissue that carries electrical messages throughout the body. It includes central nervous system and the peripheral nervous system (see Figure below). 

Central Nervous System (CNS) is composed by the:
1) Brain
2) Spinal Cord

Peripheral Nervous System (PNS) is composed by the peripheral nerves.

Nerve Cells

To understand why you can react so quickly, you need to understand about the nervous system.

Nervous tissue consists of just two basic types of nerve cells

1) neurons -  Neurons are the structural and functional units of the nervous system. They transmit electrical signals, called nerve impulses.

2) glial cells - Glial cells provide support for neurons. For example, they provide neurons with nutrients and other materials.

Neuron Structure

A neuron consists of three basic parts: 

1) cell body - contains the nucleus and other organelles

2) dendrites - extend from the cell body and receive nerve impulses from other neurons

3)  axon - a long extension of the cell body that transmits nerve impulses to other cells. The axon branches at the end, forming axon terminals. These are the points where the neurons communicates with other cells.

You can watch an animation of the parts of a neuron at this link:

Types of Neurons

Neurons are classified based on the direction in which they carry nerve impulses.

  • Sensory neurons carry nerve impulses from tissues and organs to the spinal cord and brain.
  • Motor neurons carry nerve impulses from the brain and spinal cord to muscles and glands(see Figure below).
  • Interneurons carry nerve impulses back and forth between sensory and motor neurons.

This axon is a motor neuron. It transmits nerve impulses to a skeletal muscle causing the muscle to contract.

Big Idea

  • Neurons are the structural and functional units of the nervous system. They consist of a cell body, dendrites, and axon.
  • Neurons transmit nerve impulses to other cells.
  • Types of neurons include sensory neurons, motor neurons, and interneurons.